Adapted rhythms of life. Presentation on ecology “Adaptive rhythms of life” presentation for an ecology lesson (grade 10) on the topic In Canada they treat with music from biorhythms
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§ 7 Adaptive rhythms of life
Remember
Daily allowance
and seasonal
changes in nature
Life on Earth developed under conditions of regular day and night and alternating seasons due to the rotation of the planet around its axis and around the Sun. Rhythm of the external environment creates periodicity, i.e., repeatability of conditions in the life of most species. Both critical periods, difficult for survival, and favorable ones are repeated regularly.
Adaptation to periodic changes in the external environment is expressed in living beings not only by a direct reaction to changing factors, but also in hereditarily fixed internal rhythms.
Circadian rhythms. Circadian rhythms adjust organisms to the change of day and night. In plants, intensive growth and flower blooming are timed to a certain time of day. Animals change their activity greatly throughout the day. Based on this feature, diurnal and nocturnal species are distinguished.
The daily rhythm of organisms is not only a reflection of changing external conditions. If you place a person, or animals, or plants in a constant, stable environment without a change of day and night, then the rhythm of life processes is maintained, close to the daily one (Fig. 35). The body seems to live according to its internal clock, counting down time.
The circadian rhythm can affect many processes in the body. In humans, about 100 physiological characteristics are subject to the daily cycle: heart rate, breathing rhythm, secretion of hormones, secretions of the digestive glands, blood pressure, body temperature and many others. Therefore, when a person is awake instead of sleeping, the body is still tuned to the night state and sleepless nights have a bad effect on health .
However, circadian rhythms do not appear in all species, but only in those in whose lives the change of day and night plays an important ecological role. The inhabitants of caves or deep waters, where there is no such change, live according to different rhythms. And among land dwellers, the daily frequency
not found in everyone. For example, tiny shrews alternate between activity and rest every 15-20 minutes, regardless of day or night. Due to their high metabolic rate, they are forced to eat around the clock.
In experiments under strictly constant conditions, Drosophila fruit flies maintain a daily rhythm for tens of generations. This periodicity is inherited in them, as in many other species. So profound are the adaptive reactions associated with the daily cycle of the external environment.
Disturbances in the body's circadian rhythm during night work, space flights, scuba diving, etc. represent a serious medical problem.
Annual rhythms. Annual rhythms adapt organisms to seasonal changes in conditions (Fig. 36). In the life of species, periods of growth, reproduction, molting, migration, and deep dormancy naturally alternate and repeat in such a way that organisms meet the critical time of year in the most stable state. The most vulnerable process - reproduction and rearing of young animals - occurs during the most favorable season. This periodicity of changes in physiological state throughout the year is largely innate, that is, it manifests itself as an internal annual rhythm. If, for example, Australian ostriches or the wild dog dingo are placed in a zoo in the Northern Hemisphere, their breeding season will begin in the fall, when it is spring in Australia. The restructuring of internal annual rhythms occurs with great difficulty, over a number of generations.
Preparation for reproduction or overwintering is a long process that begins in organisms long before the onset of critical periods.
Sharp short-term changes in weather (summer frosts, winter thaws) usually do not disrupt the annual rhythms of plants and animals. The main environmental factor to which organisms respond in their annual cycles is not random changes in weather, but photoperiod- changes in the ratio of day and night.
The length of daylight hours naturally changes throughout the year, and it is these changes that serve as an accurate signal of the approach of spring, summer, autumn or winter.
The ability of organisms to respond to changes in day length is called photoperiodism.
If the day shortens, species begin to prepare for winter; if it lengthens, they begin to actively grow and reproduce. In this case, it is not the factor of changing the length of day and night that is important for the Life of organisms, but
and its signal value, indicating upcoming profound changes in nature.
As you know, the length of the day greatly depends on geographic latitude. In the northern hemisphere, summer days are much shorter in the south than in the north. Therefore, southern and northern species react differently to the same amount of day change: southern species begin to reproduce with shorter days than northern ones.
Examples and additional information
1. Cave explorers - speleologists studied their daily rhythms in detail. They went down into the cave for a long period of time (1-3 months) without a watch and built their mode of work, sleep, food and rest based on their own senses of time. Communication with the surface was one-way; they did not receive any information from the outside. From the outside, their signals were carefully recorded and analyzed. It turned out that under constant conditions a person maintains a regular cycle of sleep and wakefulness, but the period of this cycle is not exactly equal to 24 hours, but may differ by several minutes. Over many days, this difference adds up, and after some time, speleologists go to bed when it is day on the surface, and stay awake at night. At the end of the experiment, it turns out that their timing does not coincide with real dates by several days.
The same results were obtained in numerous experiments with animals. Under constant conditions, their internal rhythm turns out to be not strictly circadian, but circadian; when day and night change, the external rhythm seems to correct the internal one and adjusts it to 24 hours.
2. The inhabitants of the marine intertidal zone have the most complex rhythms. Thus, off the coast of the Atlantic Ocean, water rises and falls twice a day with a period of 12.4 hours. Consequently, the exact timing of the tides gradually shifts. At low tide, the mollusks tightly squeeze their shells, and the crustaceans hide in the sand or under wet algae. In addition, this rhythm of their life is also superimposed on daily periodicity. Crustaceans and crabs are more active during daytime tides than at night.
3. In one experiment, flying squirrels were kept in cages in constant darkness. In nature, these animals are active at night and sleep during the day. With a regular change of day and night, they wake up and fall asleep at about the same time. In the experiment, each flying squirrel lived according to its own circadian rhythm, and it turned out to be slightly different in different individuals: in some it was 5-10 minutes behind the day, in others it was several minutes ahead of the day. As a result, after a certain period, a complete mismatch of general activity occurred: each animal woke up and fell asleep at its own time. When the cycle of day and night was restored, the activity of the flying squirrels returned to order.
4. Species with a wide distribution respond differently to the same day length in different parts of their range. The critical length of the day at which the growth and development of larvae in the sorrel lancet butterfly stops is 14.5 hours at the latitude of Sukhumi, 18.06 hours in the vicinity of Vitebsk, and 19.5 hours near St. Petersburg.
Tasks.
1. Draw a flower clock on a piece of paper, determining the sequence of planting different plants in the flowerbed so that you can use it to determine the time. The table shows an abbreviated list of those species from which the famous Swedish botanist Carl Linnaeus first created such a clock in the vicinity of the city of Uppsala, where he lived and worked.
2. In some particularly arid areas of Australia and Africa, native bird species do not exhibit annual breeding rhythms. They lay eggs at varying intervals immediately after infrequent rains. Explain the reasons for this exception. Should we expect photoperiodism to occur in these species?
3. Measure your heart rate using your pulse in a calm state at different times of the day (for example, at 8, 15 and 21 hours). Repeat measurements within 3-4 days. Compare the results. Is the circadian rhythm evident in your heart rate?
4. Give examples of species that you think should not have circadian rhythms and explain why you think so.
5. On the city’s boulevards, some of the poplars froze to death during the harsh winter. Trees growing near street lights were hit the hardest. Why?
Topics for discussion.
1. Many people claim that preparing for exams in silence at night is much more productive than during the day. Do you agree with this? Justify your answer.
2. If it was up to you to organize work on the night shift at enterprise, what would you choose: a) permanent night work with increased pay for those who agree to such a regime; b) alternating day and night work for each with increased rest after the night; c) only day work
In temperate or tropical climates, are there species that are most sensitive to day length?
Chernova N. M., Fundamentals of Ecology: Textbook. days 10 (11) grade. general education textbook institutions/ N. M. Chernova, V. M. Galushin, V. M. Konstantinov; Ed. N. M. Chernova. - 6th ed., stereotype. - M.: Bustard, 2002. - 304 p.
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Adaptation to periodic changes in the external environment is expressed in living beings not only by a direct reaction to changing factors, but also in hereditarily fixed internal rhythms.
Circadian rhythms
Daily allowance biorhythms organisms adapt to the cycle of day and night. In plants, intensive growth and flower blooming are timed to a certain time of day. Animals change their activity greatly throughout the day. Based on this feature, diurnal and nocturnal species are distinguished.
The daily rhythm of organisms is not only a reflection of changing external conditions. If you place a person, or animals, or plants in a constant, stable environment without a change of day and night, then the rhythm of life processes is maintained, close to the daily one (Fig. 1). The body seems to live according to its internal clock, counting down time.
Rice. 1. Daily rhythms of bean leaf movement and rat activity under constant lighting conditions in the laboratory
The circadian rhythm can affect many processes in the body. In humans, about 100 physiological characteristics are subject to the daily cycle: heart rate, breathing rhythm, secretion of hormones, secretions of the digestive glands, blood pressure, body temperature and many others. Therefore, when a person is awake instead of sleeping, the body is still tuned to the night state and sleepless nights have a bad effect on health.
However, circadian rhythms do not appear in all species, but only in those in whose lives the change of day and night plays an important ecological role. The inhabitants of caves or deep waters, where there is no such change, live according to different rhythms. And even among land dwellers, not everyone exhibits daily periodicity. For example, tiny shrews alternate between activity and rest every 15–20 minutes, regardless of day or night. Due to their high metabolic rate, they are forced to eat around the clock.
In experiments under strictly constant conditions, Drosophila fruit flies maintain a daily rhythm for tens of generations. This periodicity is inherited in them, as in many other species. So profound are the adaptive reactions associated with the daily cycle of the external environment.
Disturbances in the body's circadian rhythm during night work, space flights, scuba diving, etc. represent a serious medical problem.
Annual rhythms
Annual rhythms adapt organisms to seasonal changes in conditions (Fig. 2). In the life of species, periods of growth, reproduction, molting, migration, and deep dormancy naturally alternate and repeat in such a way that organisms meet the critical time of year in the most stable state. The most vulnerable process - reproduction and rearing of young animals - occurs during the most favorable season. This periodicity of changes in physiological state throughout the year is largely innate, that is, it manifests itself as an internal annual rhythm. If, for example, Australian ostriches or the wild dog dingo are placed in a zoo in the Northern Hemisphere, their breeding season will begin in the fall, when it is spring in Australia. The restructuring of internal annual rhythms occurs with great difficulty, over a number of generations.
Rice. 2. The annual cycle in the life of deer
Preparation for reproduction or overwintering is a long process that begins in organisms long before the onset of critical periods.
Sharp short-term changes in weather (summer frosts, winter thaws) usually do not disrupt the annual rhythms of plants and animals. Main environmental factor, to which organisms respond in their annual cycles, is not random changes in weather, but photoperiod – changes in the ratio of day and night.
The length of daylight hours naturally changes throughout the year, and it is these changes that serve as an accurate signal of the approach of spring, summer, autumn or winter.
The ability of organisms to respond to changes in day length is called photoperiodism .
If the day shortens, species begin to prepare for winter; if it lengthens, they begin to actively grow and reproduce. In this case, what is important for the life of organisms is not the change in the length of day and night itself, but its signal value , indicating impending profound changes in nature.
As you know, the length of the day greatly depends on geographic latitude. In the northern hemisphere, summer days are much shorter in the south than in the north. Therefore, southern and northern species react differently to the same amount of day change: southern species begin to reproduce with shorter days than northern ones.
One of the fundamental properties of living nature is the cyclical nature of most processes occurring in it. All life on Earth, from the cell to the biosphere, is subject to certain rhythms. Natural rhythms for any organism can be divided into internal (related to its own vital activity) and external (cyclical changes in the environment).
Internal loops. Internal cycles are primarily the physiological rhythms of the body. No physiological process occurs continuously. Rhythmicity is found in the processes of DNA and RNA synthesis in cells, in the assembly of proteins, in the work of enzymes, and in the activity of mitochondria. Cell division, muscle contraction, the work of the endocrine glands, the beating of the heart, breathing, the excitability of the nervous system, i.e., the work of all cells, organs and tissues of the body, are subject to a certain rhythm. Moreover, each system has its own period. This period can be changed by the action of environmental factors only within narrow limits, and for some processes it is not possible at all. This rhythm is called endogenous.
All internal rhythms of the body are subordinated, integrated into an integral system and ultimately act as the general periodicity of the body’s behavior. Rhythmically carrying out his
physiological functions, the body seems to count down time. For both external and internal rhythms, the onset of the next phase depends primarily on time. Therefore, time acts as one of the most important environmental factors to which living organisms must respond, adapting to external cyclical changes in nature.
External rhythms. The main external rhythms are of a geophysical nature, as they are associated with the rotation of the Earth relative to the Sun and the Moon relative to the Earth. Under the influence of this rotation, many environmental factors on our planet, especially light conditions, temperature, air pressure and humidity, atmospheric electromagnetic field, ocean tides, etc., naturally change. In addition, living nature is also affected by cosmic rhythms such as periodic changes in solar activity. The Sun is characterized by an 11-year and a number of other cycles. Changes in solar radiation significantly affect the climate of our planet. In addition to the cyclical influence of abiotic factors, external rhythms for any organism are also natural changes in the activity and behavior of other living beings.
A number of changes in the life activity of organisms coincide in period with external, geophysical cycles. These are the so-called adaptive biological rhythms - daily, tidal, equal to the lunar month, annual. Thanks to them, the most important biological functions of the body, such as nutrition, growth, reproduction, coincide with the most favorable time of day or year for this.
Adaptive biological rhythms arose as an adaptation of the physiology of living beings to regular environmental changes in the external environment. In this they differ from purely physiological rhythms that support the continuous vital activity of organisms, respiration, blood circulation, cell division, etc.
The circadian rhythm has been found in a variety of organisms, from single-celled organisms to humans. In humans, over 100 physiological functions are noted that are affected by daily periodicity: sleep and wakefulness, changes in body temperature, heart rate, depth and frequency of breathing, volume and chemical composition of urine, sweating, muscle and mental performance, etc. In amoebas, during days, the rate of division changes. In some plants, the opening and closing of flowers, the raising and lowering of leaves, the maximum intensity of respiration, the growth rate of the coleoptile, etc. are timed to a certain time.
Based on the alternation of periods of sleep and wakefulness, animals are divided into daytime and nighttime. Daytime activity is pronounced, for example, in domestic chickens, most passerine birds, ground squirrels, ants, and dragonflies. Typically nocturnal animals are hedgehogs, bats, owls, wild boars, most felines, grass frogs, cockroaches and many others. Some species are approximately equally active both during the day and at night, with alternating short periods of wakefulness and rest. This rhythm is called polyphasic (many shrews, a number of carnivores, etc.).
In a number of animals, daily changes affect primarily motor activity and are not accompanied by significant deviations in physiological functions (for example, in rodents). The most striking examples of physiological changes during the day are provided by bats. In summer, during the period of daytime rest, many of them behave like poikilothermic animals. Their body temperature at this time is almost equal to the ambient temperature; Pulse, breathing, and the excitability of the sensory organs are sharply reduced. In order to take off, a disturbed mouse warms up for a long time due to chemical heat production. In the evening and at night, these are typical homeothermic mammals with high body temperature, active and precise movements, and quick reactions to prey and enemies.
In some species, periods of activity are strictly confined to a certain time of day, while in others they can shift depending on the situation. Thus, the opening of saffron flowers depends on temperature, dandelion inflorescences - on light: on a cloudy day the baskets do not open. The activity of desert woodlice or darkling beetles shifts to different times of day depending on the temperature and humidity of the soil surface. They emerge from their burrows either early in the morning and in the evening (two-phase cycle), or only at night (single-phase), or throughout the day.
It is possible to distinguish endogenous circadian rhythms from exogenous ones, i.e. those imposed by the external environment, in an experiment. In many species, with complete constancy of external conditions (temperature, illumination, humidity, etc.), cycles that are close in period to the daily cycle continue to persist for a long time. In fruit flies, for example, such an endogenous rhythm can be traced over tens of generations. Thus, the daily cyclicity of life activity turns into the innate, genetic properties of the species. Such endogenous rhythms are called circadian (from the Latin circa - about and dies - day, day), since their duration is not the same in different individuals of the same species, slightly different from the average 24-hour period.
Flying squirrels, which are characterized by twilight activity, wake up synchronously in the evening, at a strictly defined hour. In the experiment, being in complete darkness, they maintain a circadian rhythm. However, some individuals begin their “day” a few minutes earlier; others - a few minutes later than the normal daily cycle. If, for example, the circadian rhythm is 15 minutes shorter than the daily rhythm, then for such an animal after three days the time discrepancy with the external rhythm will be 45 minutes, after 10 days - already 2.5 hours, etc. Therefore, all flying squirrels wake up after a few days and begin to move at completely different times, although each maintains the constancy of its cycle. When the cycle of day and night is restored, the animals' sleep and wakefulness are synchronized again. Thus, the external circadian cycle regulates the duration of innate circadian rhythms, coordinating them with environmental changes.
In humans, circadian rhythms were studied in various situations: in caves, hermetic chambers, scuba diving, etc. It was discovered that the typological features of the nervous system play a large role in deviations from the circadian cycle in humans. Circadian rhythms can vary even among members of the same family.
A well-known behavioral stereotype, determined by the circadian rhythm, facilitates the existence of organisms during daily changes in the environment. However, when animals and plants spread and find themselves in geographical conditions with a different rhythm of day and night, a too strong stereotype can become unfavorable. Therefore, the dispersal capabilities of a number of species are limited by the deep fixation of their circadian rhythms. For example, gray rats differ from black rats in significantly greater plasticity of the daily cycle. In black rats it is almost impossible to change, and the species has a limited range, while gray rats have spread almost throughout the world.
In most species, circadian rhythm adjustment is possible. Usually it does not occur immediately, but takes place over several cycles and is accompanied by a number of disturbances in the physiological state of the body. For example, people who fly long distances in a latitudinal direction experience desynchronization of their physiological rhythm with local astronomical time. The body first continues to function as before, and then begins to rebuild. At the same time, you feel increased fatigue, malaise, a desire to sleep during the day and stay awake at night. The adaptation period lasts from several days to two weeks.
Rhythm desynchronization is an important medical problem in organizing night and shift work for people in a number of professions, in space flights, scuba diving, underground work, etc.
Circadian and circadian rhythms underlie the body's ability to sense time. This ability of living beings is called the “biological clock”.
A number of highly organized animals have a complex innate ability to use orientation in time to orient themselves in space. Birds during long flights also constantly adjust their direction in relation to the Sun or the polarized light of the sky, taking into account the time of day. The “biological clocks” of living organisms orient them not only in the daily cycle, but also in more complex geophysical cycles of changes in nature.
Tidal rhythms. Species living in the littoral zone live in conditions of a very complex periodicity of the external environment. Superimposed on the 24-hour cycle of fluctuations in lighting and other factors is the alternation of ebbs and flows. During the lunar day (24 hours 50 minutes) there are 2 high tides and 2 low tides, the phases of which shift daily by approximately 50 minutes. The strength of the tides, in addition, naturally changes during the synodic, or lunar, month (29.5 solar days). Twice a month (new moon and full moon) they reach their maximum value (the so-called spring tides).
The life of organisms living in the coastal zone is subject to this complex rhythm. During low tide, oysters squeeze their valves tightly and stop feeding. The frequency of opening and closing the shell is maintained for a long time in aquariums. It gradually changes if the aquarium is moved to a different geographical area, and eventually settles in accordance with the new tidal schedule, although the mollusks do not directly experience their effects. Experiments suggest that the restructuring is caused by the perception by oysters of those changes in the state of the atmosphere that accompany tidal phenomena.
The silverside fish, which lives off the coast of California, uses the height of spring tides in its life cycle. At the highest tide, females lay eggs at the water's edge, burying them in sandy soil. As the water recedes, the eggs remain
ripen in wet sand. The hatching of the fry occurs after half a month and is timed to coincide with the next high tide.
Periodicity equal to the lunar month as an endogenous rhythm has been identified in a number of marine and terrestrial organisms. It manifests itself in the timing of the spawning of palolo polychaete worms, the reproduction of Japanese sea lilies, and the swarming of a number of chironomid mosquitoes and mayflies, which coincide with certain phases of the Moon. In a number of animals, a periodicity equal to the lunar month was revealed in the reaction to light, to weak magnetic fields, and in the speed of orientation. In humans, an initial connection between menstrual cycles and the synodic month is assumed; changes in the tendency to bleeding have been noted in operated patients, etc. The adaptive significance of most endogenous lunar rhythms is still unknown.
Annual rhythms are among the most universal in living nature. Regular changes in physical conditions throughout the year have caused the evolution of species to undergo a wide variety of adaptations to this periodicity. The most important of them are related to reproduction, growth, migration and surviving unfavorable periods of the year. In species with a short life cycle, the annual rhythm naturally manifests itself in a number of generations (for example, cyclomorphosis in daphnia and rotifers).
Seasonal changes represent profound shifts in the physiology and behavior of organisms, affecting their morphology and life cycle features. The adaptive nature of these changes is obvious: thanks to them, such a crucial moment in the life of the species as the appearance of offspring turns out to be confined to the most favorable time of year, and the experience of critical periods occurs in the most stable state.
The sharper the seasonal changes in the external environment, the more pronounced the annual periodicity of the life activity of organisms. Autumn leaf fall, various diapauses, hibernation, fat storage, seasonal molting, migrations, etc. are developed mainly in countries of temperate and cold climates, while in the inhabitants of the tropics the seasonal periodicity in life cycles is less pronounced.
Annual rhythms in many species are endogenous. Such rhythms are called circan (Latin annus - year). This especially applies to breeding cycles. Thus, animals of the southern hemisphere kept in zoos in the northern hemisphere breed most often in winter or autumn, at times corresponding to spring and summer in their homeland. Australian ostriches in the Askania-Nova nature reserve laid eggs in winter directly on the snow. The dingo dog gives birth to pups in December, which is the end of spring in Australia. The stability of the timing of reproduction in the annual cycle must be taken into account during the introduction and acclimatization of species.
Severe thaws in winter and frosts in summer usually do not disrupt seasonal changes in plants and animals. At the same time, the accuracy of the annual cycle is not always of an endogenous nature. For example, the seeds of a number of plants germinate at a strictly defined time of year, even after an experimentally induced state of complete anabiosis, which should disrupt the “countdown” of time in the body. Consequently, germination is stimulated by some environmental changes associated with geophysical cycles.
Currently, the response of organisms to weak geoelectromagnetic fields, as well as atmospheric ebbs and flows, which naturally change in the cycles of the Earth's rotation, is being intensively studied. It has been shown that the intensity of a number of biological processes correlates with fluctuations in these subtle indicators of the state of the atmosphere throughout the year, such as , motor activity of insects, rate of oxygen consumption by potato tubers, etc.
Thus, the onset of the next stage of the annual cycle in living organisms occurs partly as a result of endogenous rhythms, and partly caused by fluctuations in external environmental factors. It is noteworthy that the annual periodicity does not depend on powerful environmental factors directly acting on the body (temperature, humidity, etc.), which are subject to strong weather variability, but on environmental properties that are secondary to life activity, which, however, change very naturally throughout the year. The adaptive meaning of this phenomenon is that short-term changes in weather conditions, their possible significant deviations from the norm, do not change the biological rhythm of organisms, which remains synchronized with the general course of changes in nature throughout the year.
One of the most precisely and regularly changing environmental factors is the length of daylight hours, the rhythm of alternating dark and light periods of the day. It is this factor that serves most living organisms for orientation in the seasons.
Adaptive rhythms of life
Life on Earth developed under conditions of regular day and night and alternating seasons due to the rotation of the planet around its axis and around the Sun. The rhythm of the external environment creates periodicity, that is, repeatability of conditions in the life of most species. Both critical periods, difficult for survival, and favorable ones are repeated regularly.
Adaptation to periodic changes in the external environment is expressed in living beings not only by a direct reaction to changing factors, but also in hereditarily fixed internal rhythms.
Circadian rhythms. Circadian rhythms adapt organisms to the cycle of day and night. In plants, intensive growth and flower blooming are timed to a certain time of day. Animals change their activity greatly throughout the day. Based on this feature, diurnal and nocturnal species are distinguished.
The daily rhythm of organisms is not only a reflection of changing external conditions. If you place a person, or animals, or plants in a constant, stable environment without a change of day and night, then the rhythm of life processes is maintained, close to the daily one (Fig. 35). The body seems to live according to its internal clock, counting down time.
The circadian rhythm can affect many processes in the body. In humans, about 100 physiological characteristics are subject to the daily cycle: heart rate, breathing rhythm, secretion of hormones, secretions of the digestive glands, blood pressure, body temperature and many others. Therefore, when a person is awake instead of sleeping, the body is still tuned to the night state and sleepless nights have a bad effect on health.
However, circadian rhythms do not appear in all species, but only in those in whose lives the change of day and night plays an important ecological role. The inhabitants of caves or deep waters, where there is no such change, live according to different rhythms. And even among land dwellers, not everyone exhibits daily periodicity. For example, tiny shrews alternate between activity and rest every 15-20 minutes, regardless of day or night. Due to their high metabolic rate, they are forced to eat around the clock.
Disturbances in the body's circadian rhythm
In experiments under strictly constant conditions, Drosophila fruit flies maintain a daily rhythm for tens of generations. This periodicity is inherited in them, as in many other species. So profound are the adaptive reactions associated with the daily cycle of the external environment.
Disturbances in the body's circadian rhythm during night work, space flights, scuba diving, etc. represent a serious medical problem.
Annual rhythms. Annual rhythms adapt organisms to seasonal changes in conditions (Fig. 36). In the life of species, periods of growth, reproduction, molting, migration, and deep dormancy naturally alternate and repeat in such a way that organisms meet the critical time of year in the most stable state. The most vulnerable process - reproduction and rearing of young animals - occurs during the most favorable season. This periodicity of changes in physiological state throughout the year is largely innate, that is, it manifests itself as an internal annual rhythm. If, for example, Australian ostriches or the wild dog dingo are placed in a zoo in the Northern Hemisphere, their breeding season will begin in the fall, when it is spring in Australia. The restructuring of internal annual rhythms occurs with great difficulty, over a number of generations.
Preparation for reproduction or overwintering is a long process that begins in organisms long before the onset of critical periods.
Sharp short-term changes in weather (summer frosts, winter thaws) usually do not disrupt the annual rhythms of plants and animals. The main environmental factor to which organisms respond in their annual cycles is not random changes in weather, but photo-period - changes in the ratio of day and night.
The length of daylight hours naturally changes throughout the year, and it is these changes that serve as an accurate signal of the approach of spring, summer, autumn or winter.
The ability of organisms to respond to changes in day length is called photoperiodism.
If the day shortens, species begin to prepare for winter; if it lengthens, they begin to actively grow and reproduce. In this case, what is important for the Life of organisms is not the factor itself of changing the length of day and night, but its signaling value, indicating impending profound changes in nature.
As you know, the length of the day greatly depends on geographic latitude. In the northern hemisphere, summer days are much shorter in the south than in the north. Therefore, southern and northern species react differently to the same amount of day change: southern species begin to reproduce with shorter days than northern ones.
Examples and additional information
Cave explorers - speleologists studied their daily rhythms in detail. They went down into the cave for a long period of time (1-3 months) without a watch and built their mode of work, sleep, food and rest based on their own senses of time. Communication with the surface was one-way; they did not receive any information from the outside. From the outside, their signals were carefully recorded and analyzed. It turned out that under constant conditions a person maintains a regular cycle of sleep and wakefulness, but the period of this cycle is not exactly equal to 24 hours, but may differ by several minutes. Over many days, this difference adds up, and after some time, speleologists go to bed when it is day on the surface, and stay awake at night. At the end of the experiment, it turns out that their timing is several days out of line with the actual dates.
The same results were obtained in numerous experiments with animals. Under constant conditions, their internal rhythm turns out to be not strictly circadian, but circadian; when day and night change, the external rhythm seems to correct the internal one and adjusts it to 24 hours.
The inhabitants of the marine intertidal zone have the most complex rhythms. Thus, off the coast of the Atlantic Ocean, water rises and falls twice a day with a period of 12.4 hours. Consequently, the exact timing of the tides gradually shifts. At low tide, the mollusks tightly squeeze their shells, and the crustaceans hide in the sand or under wet algae. In addition, this rhythm of their life is also superimposed on daily periodicity. Crustaceans and crabs are more active during daytime tides than at night.
In one experiment, flying squirrels were kept in cages in constant darkness. In nature, these animals are active at night and sleep during the day. With a regular change of day and night, they wake up and fall asleep at about the same time. In the experiment, each flying squirrel lived according to its own circadian rhythm, and it turned out to be slightly different in different individuals: in some it was 5-10 minutes behind the day, in others it was several minutes ahead of the day. As a result, after a certain period, a complete mismatch of general activity occurred: each animal woke up and fell asleep at its own time. When the cycle of day and night was restored, the activity of the flying squirrels returned to order.
Species with a wide distribution respond differently to the same day length in different parts of their range. The critical length of the day at which the growth and development of larvae in the sorrel lancet butterfly stops is 14.5 hours at the latitude of Sukhumi, 18.06 hours in the vicinity of Vitebsk, and 19.5 hours near St. Petersburg.
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